In general, the most efficient point-to point transportation of freight combines the best features of the railroad system and the highway system. Highway vehicles are preferred for reaching most individual addresses, because of the ubiquity of the highway system. However, for long distance transportation, where cost per ton-mile is very important, the railroad system is the most efficient.
One method of exploiting the advantages of the two systems is to use highway vehicles to pick up freight at specific addresses, and then to load the highway vehicles onto railroad vehicles for long distance transportation. Subsequently, in the vicinity of the destination, the highway vehicles are off-loaded, and used to carry the freight to the final addresses.
Most commonly, the highway vehicles are tractor trailer combinations. After picking up freight at specific addresses, the tractor-trailer combinations are driven to terminals, where the trailers are uncoupled from the tractors and placed on railroad vehicles. The trailers are then carried on the railroad vehicles to terminals close to the intended destinations for the freight. The trailers are then removed from the railroad vehicles, connected to tractors and are then pulled to their destinations.
One method of loading the trailers onto railroad vehicles is to lift them by machinery such as cranes or forklifts. The required machinery for lifting the loaded trailers is very large and expensive, and the method cannot readily be used for trailers such as tankers without the addition of a large amount of structure to such trailers. This approach considerably increases the ton-miles to be carried.
Another approach to loading and unloading of highway trailers onto railway vehicles is "circus loading". In this procedure, a consist of coupled railroad cars, which may be, for example, flat cars or box cars, are moved into a position in which one end of the consist is adjacent a dock for motor vehicles. Plates are positioned on the railway vehicles so as to provide a continuous roadway between coupled railway vehicles. Tractors are used to back the trailers, one at a time, down the line of railway cars. As each trailer reaches its intended location in the train, it is uncoupled, and the tractor is then driven off. A consist including a locomotive then pulls the consist on which the trailers are carried to a destination terminal. At the destination terminal, the consist carrying the trailers is again positioned adjacent a dock for motor vehicles. Tractors are backed down the line of railroad cars, coupled to the trailers, and used to pull the trailers off the consist of railway vehicles. As during the loading operation, this also must be done one at a time. Each trailer must be secured to the railway vehicle on which it is placed, for example, by stanchions attached to the railway vehicle.
Since the procedures cited above have major disadvantages, including the disadvantages mentioned, various other methods of loading trailers onto and removing trailers from railway vehicles have been contemplated, and some of these have been employed.
One approach is to use a platform structure which is permanently attached to a railroad flatcar by a pivot which has a vertical axis. The platform structure is used for supporting a highway trailer vehicle. The platform structure may be swung about the vertical pivot to a position at an angle to the flat car that so a trailer can be moved from a dock adjacent the flat car onto the platform structure. The platform structure can then be rotated to a position parallel to the railroad vehicle for travel. Examples are U.S. Pat. No. 4,129,079 and PCT publication number WO 91/07301. One disadvantage of this approach is that the weight of the platform structure must be transported with the trailer. Another disadvantage is that the structure elevates the trailer, causing clearance problems and center of gravity problems.
An approach similar to the above employs a rotary loader attached to the dock. It is rotated so a portion of it is extended over the railway vehicle so trailers can be moved on and off of the railway vehicles. This is U.S. Pat. No. 4,483,652.
Another approach is to use a moveable ramp, which can be moved along the edge of a dock adjacent the railway vehicles, and extend bridges to a position oblique to the railway vehicles and the edge of the dock so that trailers can be moved onto and off of the railway vehicles. U.S. Pat. No. 4,190,393 employs this approach.
U.S. Pat. No. 2,920,580 provides an approach in which a consist of railway vehicles has, for each pair of adjacent railway vehicles, a common bogie supporting the adjacent ends of the two railway vehicles. The bogie is supported on two trucks, each truck having two axles. The consist is moved along a spur track which has a switch which is used to switch every other bogie onto a supplemental spur track, but to leave the remaining bogies (which alternate with the switched bogies) on the first spur. The second spur curves away from the first spur, and then curves back to run parallel to the first spur. The distance between the parallel portions of the two spurs is equal to the distance between end pivots of each of the railway vehicles. A loading dock is provided alongside each of the two spurs. The railway vehicles are moved onto the spurs until adjacent railway vehicles are parallel to each other in a jack-knifed relationship. In that configuration, they are positioned perpendicular to the loading docks, the bogies and both of the spur tracks. When the railway vehicles are in that position, trailers can be pulled from the docks onto the railway vehicles. Energy storage means are required so that the railway vehicles can be moved out of the jack-knifed configuration. This approach probably has severe problems placing the railway cars in the jack-knifed position, and bringing them out of the jack-knifed position, since tractive forces applied by a locomotive would be perpendicular to the bogies and would tend to topple them off the tracks, rather than move the bogies along the tracks. Also, this arrangement of bogies supported on trucks would waste considerable space between adjacent cars, and would add considerable weight to the rail-borne portions of the system.